本文選題：高分子　切入點(diǎn)：粘彈性　出處：《太原理工大學(xué)》2016年博士論文　論文類型：學(xué)位論文

【摘要】：高分子材料的粘彈性力學(xué)特性是其工程設(shè)計(jì)與應(yīng)用的重要基礎(chǔ)與依據(jù),隨著其在微納結(jié)構(gòu)中的廣泛應(yīng)用,發(fā)展具有高分辨率的力學(xué)性能測試方法表征其微納尺度下的相關(guān)粘彈性力學(xué)行為具有重要的現(xiàn)實(shí)意義。本文以半晶態(tài)高分子材料Polyamide 12(PA12)為研究對象,采用儀器化微/納米壓入測試系統(tǒng)對其進(jìn)行原位測試,基于壓入過程所得加載段、保載段和卸載段的測試結(jié)果,從細(xì)觀角度系統(tǒng)研究了PA12的粘彈性力學(xué)行為,并將微壓入蠕變與宏觀蠕變的測試結(jié)果進(jìn)行了對比分析。具體研究內(nèi)容與結(jié)果如下:(1)采用微壓入載荷控制法和應(yīng)變率控制法(結(jié)合連續(xù)剛度測量技術(shù),CSM)研究了加載速率及應(yīng)變率對PA12加載過程載荷位移響應(yīng)的影響。結(jié)果表明,加載過程中加載指數(shù)m是與材料硬度相關(guān)的參數(shù),m2表明壓入時(shí)材料發(fā)生軟化,而m2則表明發(fā)生硬化;恒載荷速率加載時(shí)特征應(yīng)變率與載荷速率無關(guān),而與加載指數(shù)成反比。由于塑性變形區(qū)晶體相位錯(cuò)和非晶相熱激活的混合變形機(jī)理,PA12在恒載荷速率加載時(shí)表現(xiàn)為軟化,而通過應(yīng)變率控制加載且應(yīng)變率小于0.2 s-1時(shí)材料則表現(xiàn)為硬化。基于彈性接觸理論計(jì)算卸載初始段卸載剛度的方法不再有效,研究通過接觸硬度反推其表觀卸載剛度的結(jié)果顯示卸載剛度及彈性模量隨卸載速率的增加而減小。(2)為消除卸載初始段“鼻子”現(xiàn)象所引起的彈性模量值的過高測量,基于彈性接觸理論提出一種不受加載條件影響的彈性模量計(jì)算方法。結(jié)果表明,通過給定的蠕變校正因子定義式,彈性模量值不再受卸載速率與保載時(shí)間的影響且計(jì)算過程明顯簡化;隨著保載時(shí)間和卸載速率的提高,蠕變校正因子趨近于1,經(jīng)蠕變校正后的彈性模量值為一穩(wěn)定值。(3)針對階躍加載、斜坡加載和應(yīng)變率加載三種加載方式作用后保載段的測試結(jié)果,采用唯象流變學(xué)模型分析了壓入蠕變段的粘彈性響應(yīng)。結(jié)果表明,階躍加載后保載時(shí),不同載荷條件下所得蠕變?nèi)崃考把舆t譜基本相同,表現(xiàn)為線性粘彈性特征;而對于斜坡加載,加載段材料的結(jié)構(gòu)松弛使得低速率預(yù)加載后保載所得蠕變?nèi)崃吭龃?同時(shí)隨著預(yù)加載速率的降低,延遲譜峰強(qiáng)減弱且代表小分子運(yùn)動(dòng)的延遲峰消失;對于應(yīng)變率加載后保載段的蠕變響應(yīng),隨著加載應(yīng)變率的減小,延遲峰峰強(qiáng)將顯著減弱直至完全消失。(4)為表征不同載荷壓入保載時(shí)粘彈性材料的蠕變響應(yīng),基于二次力學(xué)單元構(gòu)建了一種描述蠕變變形過程的唯象學(xué)粘彈性模型。結(jié)果表明該模型可有效預(yù)測幾何自相似尖銳壓頭壓入保載段蠕變響應(yīng)的全過程,蠕變位移和蠕變位移速率均與保載載荷的平方根成正比,而蠕變應(yīng)變率則與保載載荷無關(guān)。(5)針對宏觀與微觀蠕變參量之間的跨尺度關(guān)聯(lián)問題,分別采用常規(guī)壓縮和柱形壓頭壓入進(jìn)行蠕變測試,并與階躍加載后微壓入保載段的粘彈性參數(shù)進(jìn)行對比分析。結(jié)果表明,宏觀蠕變試驗(yàn)中PA12表現(xiàn)出明顯的非線性粘彈性特征,而微壓入試驗(yàn)所得蠕變?nèi)崃亢脱舆t時(shí)間譜峰強(qiáng)低于宏觀試驗(yàn),同時(shí)微壓入延遲時(shí)間譜線上缺少代表大分子激活運(yùn)動(dòng)的延遲峰而宏觀蠕變試驗(yàn)則缺少代表小分子激活運(yùn)動(dòng)的延遲峰。
[Abstract]:The viscoelastic mechanical properties of polymer materials is an important foundation for the design and application of the project, with its wide application in micro nano structure, characterization of mechanical properties test method with high resolution development has important practical significance to the related viscoelastic behavior of micro nano scale. In this paper, the semi crystalline polymer materials Polyamide 12 (PA12) as the research object, using the instrument of micro / nano indentation test system for in situ test, indentation process from loading section based on test results of loading and unloading section section, from the microscopic view of the viscoelastic behavior of PA12, and the test results of micro indentation creep with the macroscopic creep are analyzed. The specific research contents and results are as follows: (1) adopting micro indentation load control method and strain rate control method (with the continuous stiffness measurement technology, CSM) on the loading speed The rate and the effect of strain rate on the load displacement response of the PA12 loading process. The results show that the load index in the process of loading m parameters related to the hardness of the material, M2 shows that when pressing material softening, while M2 indicates a hardening; constant loading rate loading characteristics of strain rate and load rate, but inversely with the loading index. Due to the mixing of plastic deformation zone in crystalline phase and amorphous phase. The thermally activated deformation mechanism, PA12 in constant loading rate showed softening, and strain rate control by loading and the strain rate is less than 0.2 S-1 when the material is hard. The elastic contact theory calculation method of the initial period just uninstall is no longer valid based on the research, through contact with the apparent hardness of backstepping unloading stiffness results show unloading stiffness and elastic modulus decreases with the increase of unloading rate. (2) to eliminate the initial period of "unloading nose" phenomenon High measuring elastic modulus caused by the value of the contact put forward a kind of elastic modulus is not affected by loading conditions influence the calculation method based on the elastic theory. The results show that the creep correction factor given by the definition of elastic modulus, no unloading rate and impact load time and the calculation process was simplified; with holding time and the unloading rate is increased, the creep correction factor tends to 1, the modulus of elasticity creep values corrected for a stable value. (3) according to the step loading, ramp loading and strain rate loading three loading modes after the load test results of the phenomenological analysis of indentation viscoelastic creep segment the rheological response model. The results show that the step loading after loading, the creep compliance under different loading conditions and delay spectrum is basically the same as the linear viscoelastic characteristics; while for ramp loading, loading section material. The relaxation makes low rate after holding the pre loading creep compliance increases, and with the decrease of pre loading rate, delay and delay the peak peak intensity weakened, on behalf of small molecular motion disappears; response to creep strain rate loading after the holding period, with the decrease of strain rate, the peak will delay significantly. Until it completely disappeared. (4) the creep viscoelastic material response to characterize different load loading, two mechanical unit builds a process of creep deformation description phenomenological viscoelastic model. Based on the results show that the model can effectively predict the geometry of self similar process of sharp indentation load response. Creep, creep displacement and creep displacement rate and holding load is proportional to the square root, and the creep strain rate and holding load. (5) according to the multi-scale correlation problem between macroscopic and microscopic creep parameters, divided Don't use conventional compression and creep test of cylindrical indenter, and step loading after the micro pressure into the viscoelastic parameters of holding section were analyzed. The results show that the PA12 macro creep test shows the nonlinear viscoelastic characteristics, and micro indentation tests of the creep compliance and delay time the spectral peak intensity below the macro and micro indentation test, time delay lines represent the lack of movement and delayed peak molecular activation is the lack of macro creep tests on behalf of small molecules to activate the movement of the delayed peak.

【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：O343

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本文編號：1598250